Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Physics 3 > M7: Doppler > Flashcards

M7: Doppler Flashcards

(73 cards)

Start Studying
1
Q

block diagram for doppler instrumentation

A

TX > beam former > signal processor > image processor and sound production

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

2 parts of the signal processor for doppler

A

doppler shift detector

spectrum analyzer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

how does frequency change when we scan in 2D vs doppler

A

frequency is lower for doppler than for 2D due to more attenuation from the RBCs (Rayleigh scatter)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how many cycles per pulse does the pulser generate for doppler

why

A

5-30 cycle pulses

to improve accuracy and interact w/ the cardiac cycle longer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

doppler shift detection is the result of which process

how does it work

A

quadrature phase detector

the transmitted signal (reference signal) is duplicated and stored… the duplicated reference signals are the same except they are 1/4 out of phase w/ each other…
… the returning signal is compared to the reference signal to determine a + or – shift, which determines the resultant signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

when you see quadrature phase detector what do you think

A

think 1/4 out of phase, and trying to detect + or – changes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

where is the resultant signal sent

A

to a speaker or spectral analyzer for image processing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what does the overall doppler shift signal contain

A

contains all the shifts that occur in the sample gate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how does the spectrum analyzer work

A

it separates the individual doppler shifts from the complex beat frequency… (this is where fast Fourier transformation occurs)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

the phenomenon of fast Fourier transformation is synonymous to what

A

a prism separating the different hues that comprise white light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how is the doppler signal separated into the doppler shifted frequencies (e.g. how is the spectral doppler tracing produced)

A

fast Fourier transformation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

describe how fast Fourier transformation works

A

it analyzes the complex doppler shift signal and breaks the signal into the component or separate frequencies displaying both magnitude and amplitude

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

which axis displays magnitude

which displays time

A

mag: Y
time: X

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is the magnitude of the doppler shift

A

the amount of + or – shift

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

is a + 4 kHz doppler shift the same magnitude as a – 4 kHz shift

A

yes… refers to ‘distance’ from the baseline only… magnitudes are the same, but the sign is opposite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

factors affecting magnitude

A

RBC velocity, angle of insonation, operating frequency

e.g. everything in the doppler shift formula except C which is constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

relationship b/w doppler shift and magnitude

A

greater doppler shift = greater magnitude

directly related

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is the amplitude of the doppler shift

A

represents the number of RBCs that are contained w/in the SV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

other names for amplitude

A

brightness, power, intensity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

will two individual doppler shifts of 4 kHz have the same amplitude

A

no. they have the same magnitude but may not have the same # of RBCs moving through the SV… depends on RBC density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

how is amplitude displayed on the spectral tracing

A

Z-axis or brightness of the tracing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

factors affecting amplitude

A

RBC density
attenuation
power
gain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is the SV comprised of

A

beam width, gate length (SV size) and pulse length

as well as size in the Z axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

is the SV range gated?

what does that mean

A

yes

we know how long it takes the sound to go out the sampled depth and come back because we are able to specify a desired depth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
is the SV of PW doppler three dimensional
yes
26
does the SV size change relative to depth what happens when its placed in the far field
yes... it becomes very large due to the divergence in 3 dimensions.... there is the potential for spectral broadening and picking up signals from other vessels
27
why does aliasing occur
the velocity of the RBCs are exceeding the sampling limit of the machine w/ PW... we are exceeding the nyquist limit which is 1/2 the PRF MUST BE OVER HALF THE PRF
28
what limits the amount of sampling
depth (PRF)
29
formula for nyquist limit
NL = 1/2 PRF
30
5 ways to correct for aliasing which ones do we do
``` change the baseline increase the PRF (scale) lower the frequency increase the doppler angle switch to CW ``` the first 2
31
why cant we lower the frequency, increase the doppler angle or switch to CW to correct for aliasing
1. usually defaulted to lowest frequency already 2. increase % error 3. dont usually have correct probe, but good in the echo lab
32
describe high PRF mode
can be used when the velocities exceed the nyquist limit... allows the machine to fire the next pulse before the echos from the first pulse have come back
33
purpose of high PRF mode possible consequence
can help raise the nyquist limit range ambiguity
34
how can range ambiguity affect the spectral tracing
can cause you to pick up flow from multiple depths resulting in a complex spectral tracing that displays multiple flow profiles of vessels
35
with what type of measurements should you use a fast sweep speed why
intracycle measurements (AR, PR) due to easier caliper placement and increased accuracy for systolic events since the waveform is more spread out
36
with what type of measurements should you use a slow sweep speed why
intercycle measurements like rate and rhythm
37
describe how CW works
CW has an oscillator that produces a continuous AC voltage for motion detection.. the echo signal can be sent to a speaker to processed into an image/spectra tracing just like PW
38
newer development w/ CW probes
fire half of the crystals with pulsed to get a 2D image and the other half of the crystals w/ CW to get a CW signal... allows for 2D and CW simultaneously BUT CW STILL DOESN'T PRODUCE AN IMAGE
39
describe wall filter why is it needed
used to reject low frequencies from wall motion of pulsatile vessels.... e.g. gets rid of noise but needed b/c doppler is sensitive to ANY motion, not just moving RBCs
40
risk w/ a high wall filter
could reject real, low level echos in the lower frequency range if set to high
41
what type of info does colour doppler provide what does it include in its assessment
complete qualitative blood flow analysis over a wide field of view... combines anatomical detail from the 2d image and physiological hemodynamics w/ the colour overlay
42
other names for colour doppler (CD)
colour doppler imaging (CDI) colour flow imaging (CFI) colour flow mapping (CFM)
43
two processes required to display colour doppler what does mean for the # of pulses per scan line, whats the effect of this
first, the standard 2D process - 1 pulse per scan line second, the doppler processing - at least 3 pulses per scan line we need several pulses per scan line which has a huge affect on FR
44
what processing technique is used to produce colour doppler
autocorrelation
45
describe autocorrelation
mathematical means of rapidly determining the sign, mean, power and variance of the returning signal
46
what does the term "sign" refer to w/ colour doppler
direction of flow
47
how many doppler samples are displayed on the monitor per scan line how does this affect FR and why
100-400 dramatically reduces it b/c autocorrelation must occur at each depth along the scan line
48
typical FRs w/ colour doppler what does it depend on
5-50 Hz depends on depth and size of the field of view
49
what is ensemble length
of pulses used for each scan line for colour doppler
50
another name for ensemble length
packet size
51
another name for scan line
A-line
52
what does the colour doppler that we see represent
mean or average of the velocities present
53
how many pulses per scan line are commonly used to calculate the mean velocity for colour doppler
10-20.... need a minimum of 3 pulses
54
relationship b/w ensemble length and FR
longer ensemble length = slower frame rate
55
what 4 pieces of information does autocorrelation provide about blood flow
sign (Hue) magnitude (saturation) power (luminance) variance
56
what is hue
the colour that you see that represents the sign or direction of flow
57
If you arent getting reversal in arteries, how should you change the colour scale
lower it
58
describe saturation is it a mean
saturation is the amount of colour in a mix of white and represents the magnitude of the doppler shift or the velocity of blood yes
59
what does more white mean w/ saturation
more white = less saturated and faster flow/velocity e.g. red is more saturated than pink
60
are people more sensitive to changes in hue or changes in saturation
hue
61
describe luminance
the brightness of the hue and saturation present... it represents the power of the flow and tells us the RBC density in the field of view
62
relationship b/w # of RBCs and luminance
more RBCs travelling at the same velocity in a sample will look brighter on the display
63
what is variance how does it appear on CD
the # of velocities that diverge from the mean velocity will show all difference colours/hues based on the actual velocity, not the mean
64
advantage of a variance map
can give greater detail than the averaged velocities in a hue or saturation map (can help pin point disease)
65
what is priority
another CD control that determines whether or not the colour overlay will overwrite the low level echos
66
what happens if priority is set low | high?
low: precedence is given to non-doppler shifted weak echos high: allows the colour to overwrite the low 2D echos
67
risk if priority is set too high
colour could overwrite plaque and you miss pathology
68
describe power doppler does it display magnitude or amplitude
represents the strength of the doppler shift rather than velocity amplitude ONLY
69
advantages to power doppler
no aliasing, less dependant on angle, very sensitive to low flow states
70
disadvantages to power doppler
no direction flow speed or character information | susceptible to blooming artifact
71
other names for power doppler
energy mode | power-angio
72
w/ what type of exam might power doppler be very useful
EV, looking for stalk connecting to poly, cant get an angle
73
Another name for scale
Velocity range

Physics 3 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions